JavaScript: Teach Unused{Variable,Parameter} to ignore variables with leading underscore.

javascript/ql/src/Declarations/UnusedParameter.ql

@@ -9,7 +9,7 @@
  */
 
 import javascript
-import UnusedParameter // local library
+import UnusedParameter
 
 from Parameter p
 where isAnAccidentallyUnusedParameter(p)

javascript/ql/src/Declarations/UnusedParameter.qll

@@ -46,7 +46,9 @@ predicate isUnused(Function f, Parameter p, Variable pv, int i) {
   // functions without a body cannot use their parameters
   f.hasBody() and
   // field parameters are used to initialize a field
-  not p instanceof FieldParameter
+  not p instanceof FieldParameter and
+  // common convention: parameters with leading underscore are intentionally unused
+  pv.getName().charAt(0) != "_"
 }
 
 /**

javascript/ql/src/Declarations/UnusedVariable.ql

@@ -22,7 +22,9 @@ class UnusedLocal extends LocalVariable {
     not exists(FunctionExpr fe | this = fe.getVariable()) and
     not exists(ClassExpr ce | this = ce.getVariable()) and
     not exists(ExportDeclaration ed | ed.exportsAs(this, _)) and
-    not exists(LocalVarTypeAccess type | type.getVariable() = this)
+    not exists(LocalVarTypeAccess type | type.getVariable() = this) and
+    // common convention: variables with leading underscore are intentionally unused
+    getName().charAt(0) != "_"
   }
 }